Mobility Of Organic Contaminants Research Articles

Ozonation of dioxolanes in water: Kinetics, transformation mechanism, and toxicity

Dioxolanes, which are structural analogs to dioxane, are emerging persistent mobile organic contaminants. These compounds are frequently detected in water and wastewater, but their removal has been rarely addressed in the literature. This work systematically investigated the ozonation of two representative dioxolanes, i.e., 1,3-dioxolane (1,3-D) and 2-methyl-1,3-dioxolane (2-M-1,3-D). The degradation rates of two dioxolanes exhibited a positive correlation with both ozone dosage and solution pH increment. Specifically, direct ozone oxidation dominates the degradation of dioxolanes at slightly acidic pH, while hydroxyl radical (•OH) becomes the primary oxidant under weak alkaline condition. The second-order reaction rate constants of ozone with 1,3-D and 2-M-1,3-D were determined to be 5.48 and 8.00 M−1s−1, respectively. The reaction rate constants with •OH were 9 orders of magnitude higher, reaching (3.75-8.18) × 109 and (2.65-5.78) × 109 M−1s−1 for 1,3-D and 2-M-1,3-D, respectively. A kinetic model involving 112 reactions well simulated the degradation of 1,3-D and 2-M-1,3-D under various conditions accordingly. Eight transformation products were identified totally, and seven of them (i.e., formic acid, acetic acid, oxalic acid, formaldehyde, acetaldehyde, glyoxylic acid, and 1,2-ethanediol monoacetate) were quantified. The observed evolution of these identified degradation products concludes that the degradation of 1,3-D and 2-M-1,3-D during ozonation mainly involves H-abstraction, dimerization, ring opening, disproportionation, and hydrolysis. This work not only provides essential kinetic data of dioxolanes, but also sheds light on their potential transformation mechanisms and aquatic environment risks during ozonation process.

Transport and removal of stormwater vehicle-related mobile organic contaminants in geomedia-amended sand columns

Green infrastructure drainage systems are innovative treatment units that capture and treat stormwater. Unfortunately, highly polar contaminants remain challenging to remove in conventional biofilters. To overcome treatment limitations, we assessed the transport and removal of stormwater vehicle-related organic contaminants with persistent, mobile, and toxic (in short: PMTs) properties, such as 1H-benzotriazole, NN'-diphenylguanidine, and hexamethoxymethylmelamine (PMT precursor), using batch experiments and continuous-flow sand columns amended with pyrogenic carbonaceous materials, like granulated activated carbon (GAC) or wheat-straw derived biochar. Our results indicated that all investigated contaminants were subjected to nonequilibrium interactions in sand-only and geomedia-amended columns, with kinetic effects upon transport. Experimental breakthrough curves could be well described by a one-site kinetic transport model assuming saturation of sorption sites, which we inferred could occur due to dissolved organic matter fouling. Furthermore, from both batch and column experiments, we found that GAC could remove contaminants significantly better than biochar with higher sorption capacity and faster sorption kinetics. Hexamethoxymethylmelamine, with the lowest organic carbon-water partition coefficient (KOC) and largest molecular volume among target chemicals, exhibited the lowest affinity in both carbonaceous adsorbents based on estimated sorption parameters. Results suggest that sorption of investigated PMTs was likely driven by steric and hydrophobic effects, and coulombic and other weak intermolecular forces (e.g., London–van der Waals, H-bonding). Results from extrapolating our data to a 1-m depth geomedia-amended sand filter suggested that GAC and biochar could enhance the removal of organic contaminants in biofilters and last for more than one decade. Overall, our work is the first to study treatment alternatives for NN'-diphenylguanidine and hexamethoxymethylmelamine, and contributes to better PMT contaminant removal strategies in environmental applications.

Is sorption technology fit for the removal of persistent and mobile organic contaminants from water?

Persistent, Mobile, and Toxic (PMT) and very persistent and very mobile (vPvM) substances are a growing threat to water security and safety. Many of these substances are distinctively different from other more traditional contaminants in terms of their charge, polarity, and aromaticity. This results in distinctively different sorption affinities towards traditional sorbents such as activated carbon. Additionally, an increasing awareness on the environmental impact and carbon footprint of sorption technologies puts some of the more energy-intensive practices in water treatment into question. Commonly used approaches may thus need to be readjusted to become fit for purpose to remove some of the more challenging PMT and vPvM substances, including for example short chained per- and polyfluoroalkyl substances (PFAS). We here critically review the interactions that drive sorption of organic compounds to activated carbon and related sorbent materials and identify opportunities and limitations of tailoring activated carbon for PMT and vPvM removal. Other less traditional sorbent materials, including ion exchange resins, modified cyclodextrins, zeolites and metal-organic frameworks are then discussed for potential alternative or complementary use in water treatment scenarios. Sorbent regeneration approaches are evaluated in terms of their potential, considering reusability, potential for on-site regeneration, and potential for local production. In this context, we also discuss the benefits of coupling sorption to destructive technologies or to other separation technologies. Finally, we sketch out possible future trends in the evolution of sorption technologies for PMT and vPvM removal from water.

Synthetic and Natural Surfactants for Potential Application in Mobilization of Organic Contaminants: Characterization and Batch Study

In this paper, we investigated the abilities of five sugar-based synthetic surfactants and biosurfactants from three different families (i.e., alkyl polyglycoside (APG), sophorolipid (SL), and rhamnolipid (RL)) to dissolve and mobilize non-aqueous phase liquid (NAPL) components, i.e., toluene and perchloroethylene (PCE), adsorbed on porous matrices. The objective of this study was to establish a benchmark for the selection of suitable surfactants for the flushing aquifer remediation technique. The study involved a physicochemical characterization of the surfactants to determine the critical micelle concentration (CMCs) and interfacial properties. Subsequently, a batch study, through the construction of adsorption isotherms, made it possible to evaluate the surfactants’ capacities in contaminant mobilization via the reduction of their adsorptions onto a reference adsorbent material, a pine wood biochar (PWB). The results indicate that a synthetic surfactant from the APG family with a long fatty acid chain and a di-rhamnolipid biosurfactant with a shorter hydrophobic group offered the highest efficiency values; they reduced water surface tension by up to 54.7% and 52%, respectively. These two surfactants had very low critical micelle concentrations (CMCs), 0.0071 wt% and 0.0173 wt%, respectively; this is critical from an economical point of view. The batch experiments showed that these two surfactants, at concentrations just five times their CMCs, were able to reduce the adsorption of toluene on PWB by up to 74% and 65%, and of PCE with APG and RL by up to 65% and 86%, respectively. In general, these results clearly suggest the possibility of using these two surfactants in surfactant-enhanced aquifer remediation technology.

Organophosphate Esters in the Canadian Arctic Ocean

Eleven organophosphate esters (OPEs) were detected in surface water and sediment samples from yearly sampling (2013-2018) in the Canadian Arctic. In water samples, ∑chlorinated-OPEs (Cl-OPEs) concentrations exceeded ∑non-chlorinated-OPEs (non-Cl-OPEs) with median concentrations of 10 ng L-1 and 1.3 ng L-1, respectively. In sediment samples, ∑Cl-OPEs and ∑nonchlorinated-OPEs had median concentrations of 4.5 and 2.5 ng g-1, respectively. High concentrations of OPEs in samples from the Mackenzie River plume suggest riverine discharge as an OPE source to the Canadian Arctic. The prevalence of OPEs at other sites is consistent with long-range transport. The OPE inventory of the Canadian Arctic Ocean representative of years 2013-2018 was estimated at 450-16,000 tonnes with a median ∑11OPE mass of 4100 tonnes with >99% of the OPE inventory estimated to be in the water column. These results highlight the importance of OPEs as water-based Arctic contaminants subject to long-range transport and local sources. The high OPE inventory in the water column of the Canadian Arctic Ocean points to the need for international regulatory mechanisms for persistent and mobile organic contaminants (PMOCs) that are not covered by the risk assessment criteria of the Stockholm Convention.

Substances from Multiple Sources (SMS): The Presence of Multiple Primary and Secondary Sources of Persistent and Mobile Organic Contaminants Is an Upcoming Challenge for the Drinking Water Sector and Regulatory Frameworks.

Substances from Multiple Sources (SMS): The Presence of Multiple Primary and Secondary Sources of Persistent and Mobile Organic Contaminants Is an Upcoming Challenge for the Drinking Water Sector and Regulatory Frameworks.

Determination of Persistent and Mobile Organic Contaminants (PMOCs) in Water by Mixed-Mode Liquid Chromatography-Tandem Mass Spectrometry.

The presence of persistent and mobile organic contaminants (PMOC) in aquatic environments has become a matter of concern due to their ability of breaking through natural and anthropogenic barriers, even reaching drinking water. The presence of many of these compounds in surface and drinking water has been reported in screening studies, but there is still a lack of analytical methods capable of quantifying them. Herein, we propose a method combining mixed-mode-solid-phase extraction (MM-SPE) as preconcentration technique and mixed-mode liquid chromatography (MMLC) coupled to tandem mass spectrometry as a determination technique for the quantitative determination of 23 target PMOCs in surface and drinking water samples. When compared to reversed-phase liquid chromatography, the MMLC protocol has proven to be superior in both retentive capabilities and peak shape for ionic compounds, while performing also well for neutrals. The overall method performance was satisfactory with limits of quantification under 50 ng L-1 for most of analytes in both surface and drinking water. The relative standard deviation was lower than 20%, and the average recovery was 78 and 80% in surface and drinking water, respectively. The method was applied to 15 water samples collected in Spain, where 17 out of the 23 target PMOCs were quantified in at least one sample. Among them, 6 chemicals (e.g., benzyltrimethylammonium) are reported and/or quantified here for the first time.

Occurrence of emerging persistent and mobile organic contaminants in European water samples

The release of persistent and mobile organic chemicals (PMOCs) into the aquatic environment puts the quality of water resources at risk. PMOCs are challenging to analyze in water samples, due to their high polarity. The aim of this study was to develop novel analytical methods for PMOCs and to investigate their occurrence in surface and groundwater samples. The target compounds were culled from a prioritized list of industrial chemicals that were modeled to be persistent, mobile, and emitted into the environment. Analytical screening methods based on mixed-mode liquid chromatography (LC), hydrophilic interaction LC, reversed phase LC, or supercritical fluid chromatography in combination with mass spectrometric detection were successfully developed for 57 target PMOCs and applied to 14 water samples from three European countries. A total of 43 PMOCs were detected in at least one sample, among them 23 PMOCs that have not been reported before to occur in environmental waters. The most prevalent of these novel PMOCs were methyl sulfate, 2-acrylamino-2-methylpropane sulfonate, benzyltrimethylammonium, benzyldimethylamine, trifluoromethanesulfonic acid, 6-methyl-1,3,5-triazine-diamine, and 1,3-di-o-tolylguanidine occurring in ≥50% of the samples at estimated concentrations in the low ng L−1 up to μg L−1 range. The approach of focused prioritization combined with sensitive target chemical analysis proved to be highly efficient in revealing a large suite of novel as well as scarcely investigated PMOCs in surface and groundwater.

Identification of potentially mobile and persistent transformation products of REACH-registered chemicals and their occurrence in surface waters

Transformation of industrial chemicals might be a significant source of hitherto unknown persistent and mobile organic contaminants (PMOC, PM chemicals) present in the aquatic environment. Herein we depicted a three-step strategy consisting of (I) the prioritization of potential PMOC precursors among REACH-registered chemicals, (II) their lab scale transformation through hydrolysis, photolysis, MnO2 oxidation, and biotransformation and subsequent structural elucidation of derived transformation products, and finally (III) the assessment of their environmental relevance. The proposed procedure was utilized to investigate eleven chemicals, for nine of which a concentration reduction was observed. For six of these chemicals transformation products were at least tentatively identified and partially confirmed with a commercially available reference standard. Retrospective assessment of high-performance liquid chromatography - high-resolution mass spectrometry data as well as a target screening method for the identified TPs and some of the prioritized REACH chemicals revealed the widespread presence of the following chemicals in the environment: 2-pyrrolidone (hydrolysis product of vinylpyrrolidone), TP 216 (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-acetic acid, biotransformation product of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-ethanol), and 1,3-diphenylguanidine (prioritized chemical with experimental evidence of environmental stability). 2-Pyrrolidone was detected in 23/25 investigated surface water samples and present in concentrations of up to 400 ng/L. TP 216 was detected in 20/25 surface water samples and an additional sampling of a waste water treatment plant and the receiving surface water confirmed that TP 216 is formed in waste water treatment plants. The vulcanisation agent 1,3-diphenylguanidine was present in all investigated samples. A leaching experiment with a tire suggested that tires and thus tire wear particles are a potential source of 1,3-diphenylguanidine. With these data the depicted approach was proven successful and suitable for true unknowns like TP 216, and thus an alternative to non-target screenings or suspect-screenings with predicted TPs to identify environmentally relevant transformation products.

Screening for Polar Chemicals in Water by Trifunctional Mixed-Mode Liquid Chromatography-High Resolution Mass Spectrometry.

The presence of persistent and mobile organic contaminants (PMOC) in aquatic environments is a matter of high concern due to their capability of crossing through natural and anthropogenic barriers, even reaching drinking water. Most analytical methods rely on reversed-phase liquid chromatography (RPLC), which is quite limited for the detection of very polar chemicals. Thus, many of these PMOCs may have not been recognized as water pollutants yet, due to the lack of analytical methods capable to detect them. Mixed-mode LC (MMLC), providing the combination of RP and ion-exchange functionalities is explored in this work with a trifunctional column, combining RPLC, anion and cation exchange, which allows the simultaneous determination of analytes with extremely different properties. A nondiscriminant sample concentration step followed by a MMLC-high resolution mass spectrometry method was developed for a group of 37 very polar model chemicals with different acid/base functionalities. The overall method performance was satisfactory with a mean limit of detection of 50 ng/L, relative standard deviation lower than 20% and overall recoveries (including matrix effects) higher than 60% for 54% of model compounds. Then, the method was applied to 15 real water samples, by a suspect screening approach. For those detected PMOC with standard available, a preliminary estimation of concentrations was also performed. Thus, 22 compounds were unequivocally identified in a range of expected concentrations from 6 ng/L to 540 μg/L. Some of them are well-known PMOC, such as acesulfame, perfluorobutanoic acid or metformin, but other novel pollutants were also identified, as for example di-o-tolylguanidine or trifluoromethanesulfonic acid, which had not or were scarcely studied in water so far.

Leaching of chloride, sulphate, heavy metals, dissolved organic carbon and phenolic organic pesticides from contaminated concrete

Concrete samples from demolition waste of a former pesticide plant in Sweden were analysed for total contents and leachate concentrations of potentially hazardous inorganic substances, TOC, phenols, as well as for pesticide compounds such as phenoxy acids, chlorophenols and chlorocresols. Leachates were produced by means of modified standard column leaching tests and pH-stat batch tests. Due to elevated contents of chromium and lead, as well as due to high chloride concentrations in the first leachate from column tests at L/S 0.1, recycling of the concrete as a construction material in groundworks is likely to be restricted according to Swedish guidelines. The studied pesticide compounds appear to be relatively mobile at the materials own pH>12, 12, 9 and 7. Potential leaching of pesticide residues from recycled concrete to ground water and surface water might exceed water quality guidelines for the remediation site and the EU Water Framework Directive. Results of this study stress the necessity to systematically study the mechanism behind mobility of organic contaminants from alkaline construction and demolition wastes rather than rely on total content limit values.

Transport of sodium dodecylbenzene sulfonate (SDBS)-dispersed carbon nanotubes and enhanced mobility of tetrabromobisphenol A (TBBPA) in saturated porous media

Abstract Understanding the transport behavior of carbon nanotubes (CNTs) in porous media is essential in determining their environmental impact, especially on the fate and mobility of organic contaminants. The transport of sodium dodecylbenzenesulfonate (SDBS)-dispersed CNTs and their effects on the mobility of tetrabromobisphenol A (TBBPA) in saturated glass bead-packed columns were investigated. The behavior of single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs) were compared. A simulation was carried out using a model based on convection–dispersion equation. The results showed that MWNTs was more mobile than SWNTs under the same solution conditions through porous media. CNTs transport was controlled by surface attachment and physical straining. CNTs in the feed significantly enhanced TBBPA mobility and acted as TBBPA carriers in the column. Adsorption-desorption experiments indicated that the enhanced mobility came from the irreversible adsorption and slow desorption kinetics of CNT-associated TBBPA. The modified model was in good agreement with the transport data of CNTs in different solutions with the coefficient of determination (R2) higher than 0.93. This work demonstrates that CNTs significantly enhance the mobility of TBBPA, and this effect should be considered when assessing the fate and risk of CNTs in the environment.

Bioavailability and mobility of organic contaminants in soil: new three-step ecotoxicological evaluation.

A novel approach was developed for rapid assessment of bioavailability and potential mobility of contaminants in soil. The response of the same test organism to the organic extract, water extract and solid phase of soil was recorded and compared. This approach was designed to give an initial estimate of the total organic toxicity (response to organic extractable fraction), as well as the mobile (response to water extract) and bioavailable fraction (response to solid phase) of soil samples. Eighteen soil samples with different levels of pollution and content of organic carbon were selected to validate the novel three-step ecotoxicological evaluation approach. All samples were chemically analysed for priority contaminants, including aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), hexachlorocyclohexane (HCH) and dichlordiphenyltrichloroethane (DDT). The ecotoxicological evaluation involved determination of toxicity of the organic, mobile and bioavailable fractions of soil to the test organism, bacterium Bacillus cereus. We found a good correlation between the chemical analysis and the toxicity of organic extract. The low toxicity of water extracts indicated low water solubility, and thus, low potential mobility of toxic contaminants present in the soil samples. The toxicity of the bioavailable fraction was significantly greater than the toxicity of water-soluble (mobile) fraction of the contaminants as deduced from comparing untreated samples and water extracts. The bioavailability of the contaminants decreased with increasing concentrations of organic carbon in evaluated soil samples. In conclusion, the three-step ecotoxicological evaluation utilised in this study can give a quick insight into soil contamination in context with bioavailability and mobility of the contaminants present. This information can be useful for hazard identification and risk assessment of soil-associated contaminants. Graphical Abstract New three-step ecotoxicological evaluation by using the same organism.

Influence of anionic, cationic and nonionic surfactants on adsorption and desorption of oxytetracycline by ultrasonically treated and non-treated multiwalled carbon nanotubes

High adsorption capacity of carbon nanotubes (CNTs) may greatly determine the bioavailability and mobility of organic contaminants. The fate of contaminants adsorbed by CNTs may be substantially influenced by surfactants used both in the synthesis and dispersion of CNTs. The aim of this research was to determine the influence of surfactants (nonionic – TX100, cationic – CTAB and anionic – SDBS) on adsorption and desorption of oxytetracycline (OTC) by multiwalled carbon nanotubes (MWCNTs). The surfactants used had a substantial influence on both adsorption and desorption of OTC. The direction of changes depended clearly on the type of surfactant. In case of anionic SDBS, increased adsorption of OTC by MWCNTs was observed. The presence of TX100 and CTAB decreased the adsorption of OTC by MWCNTs significantly. The increase of OTC adsorption after ultrasonic treatment was observed in case of MWCNTs alone and MWCNTs with SDBS and TX100. However, ultrasonic treatment caused OTC adsorption decrease in the presence of CTAB. The change of pH had also an important effect on OTC adsorption in the presence of surfactants. Depending on the surfactant and pH, an increase or decrease of OTC adsorption was observed. The presence of surfactants increased OTC desorption from MWCNTs significantly as follows: SDBS = CTAB < TX100. The results obtained suggest new potential threats and constitute a basis for further research considering the bioavailability and toxicity of antibiotics in the presence of MWCNTs and surfactants.

Visualising the equilibrium distribution and mobility of organic contaminants in soil using the chemical partitioning space

Assessing the behaviour of organic chemicals in soil is a complex task as it is governed by the physical chemical properties of the chemicals, the characteristics of the soil as well as the ambient conditions of the environment. The chemical partitioning space, defined by the air-water partition coefficient (K(AW)) and the soil organic carbon-water partition coefficient (K(OC)), was employed to visualize the equilibrium distribution of organic contaminants between the air-filled pores, the pore water and the solid phases of the bulk soil and the relative importance of the three transport processes removing contaminants from soil (evaporation, leaching and particle erosion). The partitioning properties of twenty neutral organic chemicals (i.e. herbicides, pharmaceuticals, polychlorinated biphenyls and volatile chemicals) were estimated using poly-parameter linear free energy relationships and superimposed onto these maps. This allows instantaneous estimation of the equilibrium phase distribution and mobility of neutral organic chemicals in soil. Although there is a link between the major phase and the dominant transport process, such that chemicals found in air-filled pore space are subject to evaporation, those in water-filled pore space undergo leaching and those in the sorbed phase are associated with particle erosion, the partitioning coefficient thresholds for distribution and mobility can often deviate by many orders of magnitude. In particular, even a small fraction of chemical in pore water or pore air allows for evaporation and leaching to dominate over solid phase transport. Multiple maps that represent soils that differ in the amount and type of soil organic matter, water saturation, temperature, depth of surface soil horizon, and mineral matters were evaluated.

A critical review of the influence of effluent irrigation on the fate of pesticides in soil

The impact of effluent irrigation on the transformation and mobility of organic contaminants is poorly understood. The objectives of this review paper are: (i) to discuss the fundamental processes influencing the transformation and transport of pesticides in soil; (ii) to present a critical analysis of the impact of effluent irrigation on the transformation and transport of pesticides in soils; (iii) to suggest research areas that need attention. Effluent irrigation affects the fate of pesticides through its direct effect on the transformation and transport of pesticides that are already present at the irrigation sites, and its indirect effect on soil properties that are important in controlling the transformation and transport of organic contaminants. It has often been noticed that the effluent-derived dissolved organic matter (DOM) facilitates the movement of soil-borne pesticides by forming soluble pesticide complexes, and enhances their biodegradation by providing energy sources for the microorganisms that are involved in pesticide degradation. However, the results of field and laboratory experiments that examined the effect of effluent irrigation on the fate of pesticides are inconsistent; in some cases reduced mobility resulting from enhanced pesticide sorption has been observed, but enhanced pesticide mobility has also been reported. The inconsistency may be related to the inherent spatial variability of soil properties and/or the heterogeneity of effluent quality. For example, effluents vary in the nature and concentration of DOM that play a vital role in the degradation, sorption and transport behaviour of pesticides. Similarly, they vary in the concentrations of solvents and surfactants that have been shown to impact sorption and transport of organic contaminants. Field-based investigations on the impact of effluent irrigation on pesticide fate coupled with an accurate characterisation of the effluent are urgently required to assess the long-term risk associated with effluent irrigation in relation to pesticide transformation and transport.

Simulation of soil washing with surfactants

A mathematical model of soil washing that incorporates the surfactant enhanced mobilization and solubilization of organic compounds was implemented using a finite difference compositional reservoir simulator. The primary objective of the model was identification of the contributions of the various mechanisms—water displacement, surfactant mobilization and dissolution—on the removal of organic contaminants from soil. Mobilization of the organic phase was described by a reduction in the residual oil saturation caused by decreased interfacial tension. Increased aqueous solubility of organic compounds due to solubilization by surfactant micelles was modeled assuming local equilibrium. Parameters for the model were obtained from experimental measurements and literature sources. The model was implemented in a two-dimensional, two-phase system. Experimental data from surfactant flushing of columns contaminated with automatic transmission fluid and a mixture of chlorinated organics were used to evaluate the performance of the model. In most cases, the predicted organic recoveries were found to agree well with experimental results. For the surfactant sodium dodecyl sulfate, mobilization of organic contaminants was the main recovery mechanism for both waste liquids modeled. The results suggest that complete dissolution of a contaminant nonaqueous phase, rather than mobilization and subsequent vertical migration, may be difficult to achieve at the surfactant concentrations studied.

Leaching of PCB compounds from untreated and biotreated sludge-soil mixtures

Column experiments were conducted to evaluate the aqueous leachability of polychlorinated biphenyls (PCBs) from sludge-soil mixtures contaminated with PCBs and hydraulic oils. Untreated and biotreated sludge-soil samples were obtained from a two-month, pilot-scale field test of PCB biodegradation in land treatment units. Column leachate comprised mainly di- and trichlorobiphenyls. In comparison to untreated samples, column leachate from biotreated samples showed 34 to 63% reduction in PCBs; average values of total PCB concentrations in the column effluent ranged from 0.36 to 0.82 μg 1 −1 for untreated samples and 0.25 to 0.30 μg 1 −1 for biotreated samples. Only a small fraction, less than 6%, of the PCB mass in the untreated sludge-soil mixtures was removed by prolonged flushing with up to 2400–3000 pore volumes of water, suggesting long-term, slow release of PCBs at low aqueous concentrations. It should be noted that flushing rates for the column experiments were much higher than typical ground-water flow rates and the two-month period for column experiments can be qualitatively compared to a greatly extended duration for ground-water flow. The leaching of PCBs from a nonaqueous phase liquid (NAPL) in the column experiments was modelled as a predominantly dissolution-governed process based on first-order kinetics. The estimated dissolution rate coefficients ranged from 0.02 to 0.04 min −1 for various PCB homolog groups. This investigation helps support the concept of biostabilization, in which contaminated materials may be actively biotreated to remove the potentially mobile organic contaminants leaving a residual material that is more stable against leaching. Natural attenuation processes like sorption and intrinsic biodegradation further reduce the PCB leachability potential. Additional long-term monitoring of the land treatment units under passive conditions is under progress to evaluate such reductions.

Influence of pH and exchangeable cation on oxidation of methylphenols by a montmorillonite clay

Research efforts on the use of clay minerals as environmental reactants to “transform” mobile organic contaminants to stationary compounds are needed for eventual field solutions to reduce organic contaminant migration. This study addresses the oxidation of 2,6-dimethylphenol (DMP) and o-methylphenol (MP) by Na +-, Ca 2+-, Al 3+- and Fe 3+-saturated montmorillonite with pH values varying between 2 and 12. Phenolic dimers, trimers and tetramers resulting from oxidative coupling have been identified by mass spectrometry. Because of alumina sheet hydrolysis at low pH conditions, more Al is exposed at the edges of the mineral particles, thus resulting in the highest oligomer yields. The dissociated phenolic -OH group (pH > 9) is a greater benzene ring activator than the non dissociated -OH group, and shows a greater tendency for oxidation by montmorillonite. Exchangeable Fe 3+ accounts for a significant portion of the oxidizing power of clay. Simple factors such as water, exchangeable cation and pH can drastically affect the ability of clays to oxidize phenols to oligomers.

Cosolvent effects on sorption and mobility of organic contaminants in soils

Batch equilibrium and column miscible displacement techniques were used to investigate the influence of an organic cosolvent (methanol) on the sorption and transport of three hydrophobic organic chemicals (HOCs) — naphthalene, phenanthrene, and diuron herbicide — in a sandy surface soil (Eustis fine sand). Equilibrium sorption constant (K) values calculated from batch and column data exhibited an inverse log-linear dependence on the volume fraction (f c) of methanol in the mixed solvent. The slope of the log-linear plot was approximately equal to the logarithm of the ratio of the HOC solubilities in neat cosolvent and water. K values obtained from breakthrough curves (BTCs) were comparable to those estimated from equilibrium sorption isotherms. Long-term exposure to methanol-water mixtures had little effect on sorption and transport properties of the soil, but column retardation factors were influenced by the short-term solvent exposure history prior to solute elution.